The first building to rise at the new World Trade Center site has landed its first tenant, it was reported yesterday.

After months of struggling to find tenants for the 52-story 7 World Trade Center, developer Larry Silverstein is in the final stages of negotiations with American Express Financial Advisers for a 15-year lease for about 20,000 square feet.

The state Legislature helped grease the wheels by passing an incentive package last month that permanently eliminates commercial rent tax for World Trade Center tenants and gives a state rent subsidy for No. 7 that Silverstein must match

Silverstein’s failure to deliver until now had generated a list of critics who ripped the developer for the pricey $50-per-square-foot rent he has sought for the 1.7 million square foot property.

Brokers also saw the slow pace of leasing as a sign that the entire Downtown market was weak.

Since the Legislature acted, officials said, prospective tenants have been lining up.

“This is terrific news for downtown,” Assembly Speaker Sheldon Silver, a Democrat who represents lower Manhattan, told the business magazine Crain’s. “Brokers have been calling my office and we’ve had to refer them to Larry.”

A spokesman for the developer had no comment on the negotiations.

American Express Financial Advisors is an insurance annuity and investment management division that is being spun off from its parent company in a deal scheduled to be completed in September.

The super-safe building features staircases protected by 2-foot-thick walls and a security system that reads computer chips carried by all employees and visitors.